Inner height appears to be wrong - or is it me?

[ColinLondon]

It displays a height that does not correspond to screen capture.

So here's a couple of example in Chrome...

Ex 1: Inner height = 1000 Captured screen (displayed area) = 1100 Measured with screen ruler = 1100

Ex 2: Inner height = 800 Captured screen (displayed area) = 880 Measured with screen ruler = 880

What's going on?

Thanks.